SagePay payment plugin errors

-- HikaShop version -- : 4.0.1
-- Joomla version -- : 3.9.1
-- PHP version -- : 7.2.13
-- Browser(s) name and version -- : Microsoft Edge 42.17134.1.0 or any other
-- Error-message(debug-mod must be tuned on) -- : Error from Sage Pay sandbag:
The VPSProtocol field you supplied contains invalid data. It should contain the value 2.23

After finally getting some sense from the plugin and a response from the sandbag system at SagePay (I still have 0 confidence when it comes to a live integration) the Sage system is returning and error page ( test.sagepay.com/Simulator/VSPFormGateway.asp ) which states:

Form Payment Gateway
This page emulates the Form submission pages. The information sent to this page via the customer's browser in the encrypted fields are decoded here and broken down for you to check. Any errors will be reported here, along with recommendations. If there are no errors, you will be able to Proceed to the payment simulation pages.


Fields in your Form Submission POST
The following fields were included in the FORM sent to the Form submission page.
VPSProtocol: 3.00
TxType: PAYMENT
Vendor: sandboxEC
Crypt: Present - See decoded section below
Submission Errors The <b>VPSProtocol</b> field you supplied contains invalid data. It should contain the value <b>2.23</b>

This appears to relate to the SagePay version number but I don't believe this is anything I have control over. Please advise ASAP??